A pH ‐responsive O ‐carboxymethyl chitosan nanoencapsulation improves λ ‐cyhalothrin efficacy and induces sex‐specific responses in Conogethes punctiferalis

Abstract BACKGROUND Conventional pesticides suffer from poor foliar retention, rapid degradation, and high non‐target toxicity, driving the need for smarter delivery systems. To address these limitations, we encapsulated λ ‐cyhalothrin in O ‐carboxymethyl chitosan (LC@O‐CMCS), and comprehensively evaluated its physicochemical properties, insecticidal activity and safety. RESULTS LC@O‐CMCS exhibited spherical morphology, uniform pesticide encapsulation, and pH‐dependent release characteristics, with 40.12% cumulative release at pH 8.0 after 168 h. LC@O‐CMCS significantly enhanced foliar deposition and wettability on litchi leaves, prolonging the field half‐life from 8.11 to 14.17 days compared to free LC. Bioassays against Conogethes punctiferalis demonstrated stage‐specific efficacy of LC@O‐CMCS, with lower median lethal concentration (LC 50 ) values than free LC for larvae (0.43 mg/L versus 0.50 mg/L), female (0.99 mg/L versus 1.36 mg/L) and male (0.53 mg/L versus 0.69 mg/L) adults. Transcriptomic analysis revealed significant sex‐specific responses. Free LC induced 139 differentially expressed genes (DEGs) in male moth and 3495 DEGs in female, while LC@O‐CMCS treatment caused 7642 DEGs in male and 1107 DEGs in female. The carrier O‐CMCS alone caused negligible DEGs in each sex, confirming that the observed sex‐dependent transcriptional changes are attributable to the nanoformulation rather than to the carrier material itself. Detoxification enzyme activities were induced exclusively in female moths, with no corresponding induction observed in males, confirming a clear sex‐specific response. Notably, LC@O‐CMCS reduced acute contact toxicity to Eocanthecona furcellata by about 11‐fold. CONCLUSION These findings demonstrate that O‐CMCS‐based nanodelivery enhances insecticidal performance through optimized physicochemical properties and sex‐specific mechanisms, offering a sustainable strategy for precision pest management. © 2026 Society of Chemical Industry.